It is fundamentally known that in the maritime area, many watercraft have autopilot systems. These are automatic control systems which are frequently configured to be software-based and computer-implemented and which hold the watercraft on a predefined course during the trip. Such autopilot systems normally have position reference sensors or other types of position determining devices such as, for example, GPS receivers, gyro compasses or similar. In addition, other parameters can be made available to the autopilot system, which can be determined and relayed, for example, by local measuring devices on the watercraft. In the present context, the term “watercraft” is to be understood as any vehicle which is intended for movement on or in the water (e.g. ships, mobile drilling rigs, etc.). The autopilot systems further normally comprise a control device which is configured to control the manoeuvring system of a watercraft. Manoeuvring systems, in particular in ships, can in particular comprise a combination of a propulsion unit, for example, a ship's propeller and a control unit, for example, a rudder system with an adjustable rudder. In such manoeuvring systems, the autopilot systems are frequently configured in particular to control or adjust the rudder and can thus calculate the actual course of the watercraft on the basis of the parameters supplied to the autopilot system and the predefined algorithms.
Furthermore, dynamic positioning systems for watercraft are known from the prior art. These are generally computer-controlled systems for the automatic positioning of watercraft, in particular ships. Dynamic positioning can either be accomplished absolutely—i.e. the watercraft is held at a fixed point above the seabed—or relative to a moving object such as a ship or a submarine vehicle. Such dynamic positionings are frequently used in the offshore oil industry for drilling platforms or other offshore watercraft. However, ships, for example, cruise ships, are now increasingly being fitted with dynamic positioning systems. These systems can furthermore additionally include autopilot functions and can thus hold watercraft on a specific, predefined course. In principle, watercraft can also have a dynamic positioning system and in addition a separate autopilot system. Such dynamic positioning systems normally comprise, inter alia, position reference sensors or other types of position determining devices such as, for example, GPS receivers, gyro compasses or similar. These devices deliver watercraft position data to the dynamic positioning system. Other such devices can be motion sensors by which means, for example, the rolling or pitching of a ship can be determined. As well as an autopilot system a dynamic positioning system comprises a control device which is configured to control the manoeuvring system on the basis of the parameters supplied to the dynamic positioning system and the algorithms stored therein. In this case the control of the manoeuvring system is usually accomplished in such a manner that a predefined position should be held. In the case of manoeuvring systems comprising both a rudder system and a propulsion unit, dynamic positioning systems are frequently capable of controlling both subsystems. Both the dynamic positioning systems and the autopilot systems for watercraft can be subsumed under the generic term automatic control systems for watercraft.
In addition, dynamic positioning systems normally further comprise at least one measuring device for determining measurement data of physical quantities of the watercraft or of physical quantities acting on the watercraft. Autopilot systems can also comprise such measuring devices. In this case, it is for example known to determine the wind strength acting on the ship with the aid of measuring devices configured as wind sensors. Alternatively or additionally, it is further known to determine the swell by means of suitable wind devices. In this respect, the at least one measuring device and the means for determining watercraft position data provide information for a central control device, for example, a computer, with reference to the position of the ship and the extent and direction of action of certain environmental forces which (can) influence the position of the watercraft. On the basis of these parameters and information on a desired course, a processing unit of the dynamic positioning system and/or of the autopilot system, which can be integrated in the control device, calculates on the basis of one or more predefined algorithms the necessary control parameters on which basis the control device relays control signals to the manoeuvring system of the ship or the watercraft and thereby influences this accordingly. By this means the desired course of the watercraft can be held or the predefined position reached or held.
The manoeuvring system of a watercraft can, for example, comprise a rudder system and a propulsion unit, in particular a propulsion propeller. The rudder system in turn generally comprises a rudder and a rudder adjusting device, in particular a steering engine. By controlling the adjusting device and the propulsion unit, the thrust and the rudder angle of the watercraft or of the manoeuvring system can be varied and the direction of travel and speed of the watercraft thereby influenced.
It is now determined by known autopilot systems or dynamic positioning systems at a given time that the course or the position of the watercraft must be changed on the basis of the present watercraft position and measurement data, the manoeuvring system is controlled and the drive power (thrust) and/or the rudder angle is altered, but frequently not at the optimal level. As a result, the course of the watercraft is frequently changed beyond the desired course or the desired position is not reached directly so that the craft must then be steered again in the opposite direction. In practice, this results in frequent controlling or adjustment of the rudder angle and possibly in a continuous change in the performance of the propulsion propeller within relatively short time intervals. This process is designated as “switching hysteresis” and has the result that the manoeuvring system is excessively stressed or the desired course or the desired position is only set with a delay. In other words, this can lead to increased abrasion or increased wear of the manoeuvring system and can have the result that the course taken by the ship is frequently not optimal. Furthermore, in the case of autopilot systems the required propulsion energy of the watercraft is increased due to the frequent rudder deflections.